Attachment method for microfluidic device

ABSTRACT

In embodiments, a silicon part and a titanium part may be soldered together without breakage or instability. In embodiments, silicon and titanium may be soldered together with a soft solder joint including indium silver, where the temperature excursion between solder solidus and use temperature limits the strain between the two surfaces. In embodiments a silicon micropump surface may be treated to remove its silicon oxide coating, and then Ti—W, Nickel, and gold layers successively sputtered onto it. A corresponding titanium manifold may be ground flat, and plated with electroless nickel. The nickel plated manifold may then be baked, so as to create a transition from pure Ti to Ni—Ti alloy to pure Ni at the surface of the manifold, and for protection of the upper Ni surface, a layer of gold may be added. The two surfaces may then be soldered in forming gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/524,373, filed on Jun. 23, 2017, the entiredisclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to methods for attachment ofMEMS pumps and other microfluidic components in implantable medicaldevices. In particular, methods are disclosed for attaching variousmicrofluidics devices made from silicon, ceramic or glass to metallicstructures made from titanium, stainless steel, cobalt alloys, or othermetals used in the construction of such devices.

BACKGROUND OF THE INVENTION

Using a silicon MEMS micro-pump in an implantable device requirespermanently connecting a silicon surface of a piezoelectric transducerto a metal manifold, such as a titanium manifold. This involves joiningtwo materials, silicon and titanium, that do not solder to each other,or to known solders or braze materials, either. This is because thesematerials do not adhere to common soldering and brazing materials, andif they did, there would be large mismatch in the co-efficient ofthermal expansion (CTE) that would put an unreasonable stress on thejoint—causing it to be weak or to fracture. In implantable devices,fractures are intolerable, inasmuch as the joint to a medical devicemust be hermetic to prevent water diffusion into the device's sensitiveelectronics portion. It must also reliably seal the inlet from theoutlet so that there is no possibility of fluid from the inlet sidepassing directly to the outlet by bypassing the micropump. It is notedthat it is cost effective to design MEMS micropumps with a minimumnumber of silicon layers, with a base layer incorporating an inletopening and an outlet opening. The inlet and the outlet must be sealedsecurely to the corresponding conduits on the titanium medical device.

Therefore, what is needed in the art are techniques to hermetically bondsilicon surfaces of MEMS micropumps to metallic (e.g., titanium)manifolds in MEMS pumps, so as to facilitate their use in implantabledevices.

SUMMARY OF THE INVENTION

Methods for joining a MEMS chip to a titanium manifold, and relatedsystems are presented. In embodiments, the joining of a silicon part toa titanium part is such that the parts do not break apart due to aco-efficient of thermal expansion (CTE) mismatch. In embodiments,silicon and titanium may be soldered together with a soft solder jointusing indium silver, where the temperature excursion of approximately120° F. between the solder solidus and the use temperature limits thestrain between the two surfaces. Because silicon and titanium cannot bedirectly soldered together, in embodiments both surfaces must first beprepared. The silicon micropump surface may be treated with hydrofluoricacid to remove its silicon oxide coating, and then Ti—W, Nickel, andgold layers successively sputtered onto it. The manifold may be groundflat, and plated with electroless nickel. The nickel plated manifold maythen be baked, so as to create a transition from pure Ti to Ni—Ti alloyto pure Ni at the surface of the manifold. To protect the upper Nisurface, a layer of gold may be added. Following these preparations, thetwo surfaces may be soldered in forming gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 depicts a top view of an exemplary implantable device with a MEMSpump, using an example attachment method in accordance with variousembodiments;

FIG. 2 shows the exemplary implantable device of FIG. 1 with atransparent cover to illustrate the interior components, and an arrowpointing to an exemplary MEMS pump assembly;

FIG. 3 depicts the MEMS pump assembly as provided in the example devicein a magnified view;

FIG. 4 depicts a perspective view of the MEMS pump assembly asabstracted from the exemplary device and seen in isolation;

FIG. 5 depicts the exemplary MEMS pump of FIG. 4, with the pump capremoved, showing the piezoelectric actuator, in accordance with variousembodiments;

FIG. 6 depicts an exploded view of the MEMS pump assembly of FIG. 4

FIG. 7 depicts the exploded view of FIG. 6 from a perspective looking upfrom underneath the assembly;

FIG. 8 depicts a top view of the exemplary MEMS pump assembly of FIG. 4;

FIG. 9 depicts a top view of the exemplary MEMS pump assembly of FIG. 5,with the pump cap removed;

FIG. 10 depicts the view of the MEMS pump assembly of FIG. 9, with thepiezoelectric MEMS micropump, including its piezoceramic actuator shownin transparency so that the components below may be seen (the pink frameis an exemplary solder preform);

FIG. 11 depicts a rear view of the exemplary MEMS pump assembly of FIG.4;

FIG. 12 depicts a front perspective view of the exemplary MEMS pumpassembly of FIG. 4;

FIG. 13 depicts a perspective view of the exemplary implantable devicefrom a point of view above the device and somewhat in front of it, wherethe large white disc is a piezoceramic tone transducer to produceaudible alarms and alerts from the pump;

FIG. 14 depicts the exemplary MEMS pump assembly as positioned on top ofthe Medication Reservoir, with no other components shown (essentiallythe view of FIG. 13 with all other components on top of the MedicationReservoir removed);

FIG. 15 depicts a side view into a vertical cut-away of the exemplarydevice of FIG. 14, where the vertical slice was made through the centerof the device—and through one half of the MEMS pump assembly, allowing aview into the reservoir and into the MEMS pump;

FIG. 16 depicts a top view of the cut away of FIG. 15;

FIG. 17 depicts a cut-away of the exemplary device of FIG. 14, but hereshowing the other side of the device than is depicted in FIG. 16;

FIG. 17A illustrates three alternate joints that may be used to join anexemplary silicon pump to a Titanium manifold, in accordance withvarious embodiments;

FIG. 17B depicts an exploded detail view of a pump assembly, O-rings,manifold and circuit connection board, in accordance with variousembodiments;

FIGS. 17C through 17E illustrate further details of each alternate jointof FIG. 17A, in vertical cross-sectional views;

FIG. 17F illustrates exemplary inlet and outlet filters for a MEMS pump;

FIGS. 17G and 17H illustrate an alternate embodiment using an adhesive(dispensed or pressure sensitive layer) to attach a filter, thusproviding an alternative to the O-rings used in the embodiment shown inFIGS. 1-17;

FIG. 17I is a photograph of an actual MEMS pump attached to a titaniummanifold, in an embodiment similar to that of FIGS. 1-17, shown herewithout the springs or pump cover;

FIG. 18 depicts an alternate example of attaching a MEMS pump to atitanium manifold, in accordance with various embodiments, showing theMEMS pump assembly on top and the titanium manifold on the bottom of thefigure, each with a layer to be attached to the top and bottom surfacesto be joined;

FIG. 19 depicts the MEMS pump assembly and the titanium manifold of FIG.18 with their respective preparatory surfaces attached;

FIG. 20 depicts the MEMS pump assembly and the titanium manifold of FIG.19 from a different perspective view;

FIG. 21 depicts an alternate gasket-less embodiment, where the MEMS pumpis provided with a gold “monorail” surrounding each of the inlet andoutlet of the pump;

FIG. 22 illustrates the MEMS pump assembly and the titanium manifold asseen in FIG. 21 from a different perspective, showing the upper surfaceof the manifold with an indium plate layer on its top surface;

FIGS. 23 and 24 illustrate a similar process as that described inconnection with FIGS. 1-17, using silicone rubber gaskets to seal aroundthe pump inlet and outlet, and the pump assembly, now having been goldplated on its bottom surface, ready to be attached to the upper surfaceof the titanium manifold, which itself has been plated with indium;

FIG. 24 depicts the two components or subassemblies of FIG. 23 now fullyattached, the process complete;

FIG. 25 depicts another alternate process for joining a MEMS pump to atitanium manifold, using a glass frit preform; an exploded view of thetwo subassemblies (MEMS pump and titanium manifold) is depicted, priorto joining; and

FIG. 26 depicts the same exploded view of FIG. 25 from a differentperspective.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description refers to the accompanying drawings.The same reference numbers may be used in different drawings to identifythe same or similar elements. In the following description, for purposesof explanation and not limitation, specific details are set forth suchas particular structures, architectures, interfaces, techniques, etc.,in order to provide a thorough understanding of the various aspects ofvarious embodiments. However, it will be apparent to those skilled inthe art having the benefit of the present disclosure that the variousaspects of the various embodiments may be practiced in other examplesthat depart from these specific details. In certain instances,descriptions of well-known devices, circuits, and methods are omitted soas not to obscure the description of the various embodiments withunnecessary detail.

Various operations may be described as multiple discrete actions oroperations in turn, in a manner that is most helpful in understandingthe claimed subject matter. However, the order of description should notbe construed as to imply that these operations are necessarily orderdependent. In particular, these operations may not be performed in theorder of presentation. Operations described may be performed in adifferent order than the described embodiment. Various additionaloperations may be performed or described operations may be omitted inadditional embodiments.

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous.

As used herein, including in the claims, the term “circuitry” may referto, be part of, or include an Application Specific Integrated Circuit(ASIC), an electronic circuit, a processor (shared, dedicated, orgroup), and/or memory (shared, dedicated, or group) that execute one ormore software or firmware programs, a combinational logic circuit,and/or other suitable hardware components that provide the describedfunctionality. In some embodiments, the circuitry may be implemented in,or functions associated with the circuitry may be implemented by, one ormore software or firmware modules. In some embodiments, circuitry mayinclude logic, at least partially operable in hardware.

The present invention relates generally to methods for attachment ofMEMS pumps and other microfluidic components in implantable medicaldevices. In particular, methods are disclosed for attaching variousmicrofluidics devices made from silicon, ceramic or glass to metallicstructures made from titanium, stainless steel, cobalt alloys, or othermetals used in the construction of such devices. The methods presentedmay be used in the construction of, for example, implantable devicesthat dispense insulin, therapeutics or other chemicals, of varioustypes. Medical devices of this type may also pump body fluids into achamber for measurement of various analytes including glucose orinsulin. They may also transport body fluids for other purposes such aspressure equalization for hydrocephalus. They may also be used to pump aworking fluid. For example, for a corrosive chemotherapeutic agent, onemight pump silicone oil into a bladder within a medication reservoir.This would force the chemotherapeutic agent out of the medicationreservoir without corroding the pump. One type of such implantabledevices utilizes MEMS pumps to dispense the insulin. In particular, thepresent invention presents a novel method for attaching a silicon MEMSpump to a titanium reservoir.

Embodiments disclosed herein may be useful for attaching microfluidicsdevices made from silicon, ceramic or glass, to metallic structures madefrom titanium, stainless steel, cobalt alloys, or other metals, used inthe construction of a microfluidics device.

In embodiments, possible device applications may include a micropump, apressure sensor, a flow sensor, thermal dilution, Coriolis, a pressuredrop across a restriction, a capillary flow restrictor, an opticalmeasurement device, an electrochemical measurement device, a flowregulator, a filter, an air vent, or a pressure reference conduit forpressure operated valve or a regulator, for some non-limiting examples.

In embodiments, a method for joining a MEMS chip to a titanium manifold,and a system including such a joint may be provided. The system andmethod may be based on a technique for joining a silicon part to atitanium part, where, unlike conventional attempts, the silicon andtitanium components do not break apart due to a thermal expansioncoefficient (CTE) mismatch. In embodiments, silicon and titanium may besoldered together using an indium silver solder. Indium silver is soft,and thus can absorb the strain resulting from the thermal expansionco-efficient mismatch. Moreover, the low melting point of theindium-silver solder limits the CTE strain by limiting the temperatureexcursion from solidus to room temperature. Because silicon and titaniumcannot be directly soldered together, in embodiments both surfaces mayfirst be prepared for soldering. Beginning with the MEMS micropumpdevice, the silicon may be treated with hydrofluoric acid to remove itssilicon oxide coating and to optimize the adhesion of the sputteredlayers. Then, immediately before the silicon oxide layer reforms, thesilicon surface may be sputtered with Titanium Tungsten Alloy (TiW),Nickel, and Gold, in that order. The TiW may act as an adhesion promoterto the silicon, the nickel as the substrate for soldering to, and thegold may prevent oxidation of the nickel surface. It is noted that thegold may dissolve away during the soldering process. The opposingsurface on a metallic manifold (e.g., titanium) may be plated withelectroless nickel, which by itself does not adhere strongly totitanium. However, when the nickel is baked, for example at 400 degreesCelsius, it may alloy with the titanium and become strongly adhered.Following that, the nickel surface may be cleaned with ammoniumhydroxide and sputtered with a second layer of nickel. The second nickelcoating may then be immediately sputtered with gold to prevent oxidationof the nickel surface. After these preparations, the two surfaces may besoldered in forming gas using an indium silver solder.

FIGS. 1-17 illustrate a MEMS pump provided in an exemplary implantabledevice, here the PhysioLogic ThinPump™, an implantable infusion pumpdispensing insulin. The device has a reservoir filled with medication,and a MEMS micropump that is joined to the reservoir so that it can drawinsulin out of the reservoir and pump the medication into the body.These connections must be hermetic to a leak rate of 10⁹ cc/sec ofhelium to prevent diffusion of water and a gradual accumulation ofmoisture that will lead to corrosion, dendrite formation and shortcircuits on the microelectronics assembly. As a general rule this meansthat the joining process cannot be polymer based. A hermetic seal ofthis type generally requires a metallurgical joint or a glass to metalseal.

As noted, FIGS. 1-17 (and FIG. 6 in particular) illustrate various partsof an exemplary MEMS pump. In conjunction with these figures, a systemand method are next described for joining the MEMS chip to a titaniummanifold. At the highest level it is noted that there are two designconstraints for such a MEMS pump. First, the separation between inletand outlet must be absolute. This is because if it were not, thenleakage from the inlet to the outlet would bypass the pump and itsvalving; this would create a situation where if a clinician were to fillthe pump and leave it in a positive pressure condition, flow throughthis leak would drive unrequested medication forward into a patient. Itis here noted that the consequences of free flow of this type can bepotentially lethal. So, in embodiments, a redundant seal may be providedusing O-rings. It is here noted that a compressed elastomeric O-ringcreates a reliable fluidics seal because of the compression of therubber seals in spite of minor surface imperfections. Alternatively apressure sensitive adhesive (as illustrated in FIGS. 17G and 17H) canalso work in this application because it too can also seal in spite ofminor surface imperfections. An additional advantage to using a pressuresensitive adhesive is that by separating the inlet seal from the outletseal, the assembly can be verified for inlet and outlet sealing using ahelium leak test. However, the O-ring seal has the advantage that it canbe used in locations where there is no opportunity for a visualverification of a seal. The O-ring seal can also seal reliably in spiteof a minimal distance between the inlet and the outlet. In fact, twoO-rings can be fit in a spacing of 0.028 inches between inlet andoutlet, as shown for example, in FIG. 10. Thus, in the depictedembodiment of FIG. 10, a redundant rubber seal is used.

As a second MEMS pump design constraint, it is also necessary tohermetically seal the entire pump and manifold assembly fluid path awayfrom any nearby compartment containing microelectronics. This requires ametallurgical joint to achieve the required level of hermeticity. Evendiffusion through a rubber gasket is absolutely not acceptable—watervapor will likely pass through a rubber gasket and will then corrode theelectrically active traces and components on the printed circuit boards,leading to device failure. So, to address both issues, in embodiments aMEMS pump may have both a mechanical attachment in the form of ametallurgic joint, and a 2× redundant rubber seal. Various embodimentsdescribed herein have both such a seal as well as a metallurgical joint.

As can be seen with reference to FIGS. 1-3, in the exemplary implantabledevice shown there is a MEMS chip 210 provided under a pump cap. Asshown in FIG. 4, such a pump cap 410 may hold the piezoelectric actuatordown (i.e., piezo 515 in FIG. 5, 615 in FIG. 6) and the pump cap maycompress the double seal (in this embodiment achieved using O-rings)against manifold 640 (FIG. 6). Pump cap 410 may be made of aluminum, orfor example, steel. While steel is a better choice because it is stiffer(notably, the Youngs modulus of Aluminum=10×10⁶ psi, whereas that ofSteel=30×10⁶ psi) aluminum is less costly. In embodiments, the entireassembly may be pulled together by two springs 510, 610. These springsattach to the pump cap 410, shown in FIG. 4, and also to the manifold,as seen in FIG. 5. In embodiments they are designed to overcome theexpansive force of the double O-ring seal as well as any force generatedby injection of medication at high pressure into the medicationreservoir—which would otherwise tend to put the solder joint undertension. With the springs in place, tension is thus precluded from themetallurgical joint between the MEMS chip and the manifold. In exemplaryembodiments of the present invention, the O-ring can provide two sealsbetween inlet and outlet, as shown in FIG. 10, for example.

FIG. 6 depicts in detail various parts of a MEMS pump according toembodiments. FIG. 6 is this an exploded view of the fully assembled MEMSpump as shown in FIG. 4. Referring to FIG. 6 there are shown a Pump Cap605, which, as noted above, fits over the MEMS pump assembly, as shownin FIG. 4. In particular, Pump Cap 605 sits on Piezoelectric Actuator615, which itself is mounted on Manifold 640, with, for example, anIndium Preform 635 between them, the latter used to solder the twosurfaces together after the preparations as described below. Springs 610also connect the Pump Cap 605 to Manifold 640, as shown in FIG. 4, andalso as seen from a top view in FIG. 8, and a side perspective view inFIG. 11. Theses springs push Piezoelectric Actuator 615 and Manifold 640together, which, as noted above, overcomes the expansive force of thedouble O-ring seal between them, as well as any force generated byinjection of medication at high pressure into the medicationreservoir—which would otherwise tend to put the solder joint between thetwo under tension. Finally, there are also shown Pre-filter 655, OutletFitting 620 and Outlet Tube 650, as well as Circuit Connection Board630. These various parts are also shown in various perspectives, invarious stages of attachment, or in various sectional views, in theremaining FIGS. 7-17.

Joining Silicon to Metal

As shown in FIGS. 1-17, an exemplary MEMS pump is joined to a manifold.It is here noted that this joining presents a significant challenge, injoining a silicon part (MEMS) to a titanium part (manifold) and nothaving the two components break apart due to CTE mismatch. As notedabove, to the inventor's knowledge, in every case where such joining wasattempted, the effort failed precisely because of the thermal expansionco-efficient mismatch. For example, one such effort is described inKager, Simone, Verbindungstechnik für die hermetische Einkapselung einesfluidischen Augenimplantats, Masterarbeit am Lehrstuhl fürMedizintechnik der TU München in Zusammenarbeit mit von Frau SimoneKager, Matrikelnummer: 3601768, Studienfach: Maschinenwesen (Sep. 30,2014). In the attempts to join silicon and titanium therein described,the CTE mismatch was an insurmountable obstacle. Thus, the bond betweenthe silicon and the titanium failed spontaneously, and the device justblew apart and broke. The present disclosure solves this problem with anovel process, next described.

The CTE mismatch between any two materials is amplified by thetemperature excursion through which they are taken. Thus, the key tosolving this problem is to find a solder that melts at a sufficientlylow temperature such that the temperature excursion In exemplaryembodiments of the present invention, the two components—metal andsilicon—may be joined by performing a soft solder joint using indiumsilver. In embodiments, the solder may comprise 97% Indium and 3%silver, for example, which results in a very low temperature solder. Itis also actually fairly soft, and may thus accommodate any straingenerated due to CTE mismatch. The temperature excursion from a roomtemperature of 25° C. to the solidus point of the solder (forIndium-silver solidus is at 143° C.) which is needed to melt the solderis not enough to develop a lot of strain between the two surfaces, whichis a key consideration in choice of solder. See, for example,http://www.indium.com/solder-alloy-guide/results.php (Indalloy #290);http://www.cleanroom.byu.edu/CTE_materials.phtml,http://www.indium.com/solder-alloy-guide/results.php (Indalloy #290). Itis noted that solidus is the highest temperature at which an alloy isstill completely solid.

Strain Acting Through the Solder Joint

It is also noted that the actual stress in the solder is inverselyproportional to the solder thickness, and requires a calculation of thestress map of the sandwich. It may thus take into account the CTE of thesolder, 22 ppm.

The coefficient of thermal expansion is often defined as the fractionalincrease in length per unit rise in temperature. It is noted that theexact definition varies, depending on whether it is specified at aprecise temperature (true coefficient of thermal expansion or a-bar) orover a temperature range (mean coefficient of thermal expansion or a).It is noted that the true coefficient is related to the slope of thetangent of the length versus temperature plot, while the meancoefficient is governed by the slope of the chord between two points onthe curve. Accordingly, variation in CTE values can occur according tothe definition used. When a is constant over the temperature range thena=a-bar. Finite-element analysis (FEA) software such as, for example,NASTRAN (MSC Software) requires that a be input, not a-bar.

The following example calculation illustrates shear strain actingthrough solder in a example Titanium to Silicon soldered joint usingindium-silver solder, in accordance with various embodiments:

Calculate the CTE Difference Between the Two:

Ti 9.5 CTE (ppm/° C.)−Si 2.6 CTE (ppm/° C.)=6.9 ppm/° C. difference inCTE

6.9*ΔT=6.9*[143 C (solidus)−25 C (room temperature)]=C*118 degrees

6.9 ppm/degrees×118 degrees=814 ppm difference in normal strain betweenthe silicon and the titanium.

It is noted that the difference in displacement is a maximum at theedges. Moreover, the strain is generally equal and opposite for eachedge, so that the relative displacement at the center is 0. For thisreason, in embodiments, the relative displacement may be calculatedusing half of the width of the chip, or 3.5 mm.

Using the 814 ppm figure derived above:

0.0814 percent×3.5 mm=3.5×0.0814=0.00285 mm or 2.85 microns.

In embodiments, a preferred thickness for a solder joint may thus be 25to 250 microns. Thus, for a device that is a square with a length of 7mm per side, and with a solder joint thickness of 25 microns, shearstrain would be arc tan(relative displacement/thickness). Shear strainis thus the infinitesimal angular displacement of any element in thesolder:

Shear strain=arc tan(2.84/25)=0.1113 radians.

It is noted that an elastic calculation of the stress level may generatea stress in excess of the yield strength for the solder material(approximately 400-600 psi for the example In97 Ag3 solder provided bythe Indium Company used in tests run by the inventor). Thus, inembodiments, actual stresses may be derived experimentally. It is notedthat for the example In97 Ag3 solder used in tests run by the inventor,the elongation to break in tension solder was seen at 50%. The empiricalinformation thus supports a 10 mil thickness of In97 Ag3 for packagesless than 10 mm in dimension, as per the Indium Corporation, themanufacturer of the example solder used.

Soldering to Each of Titanium and Silicon

A. Preparing the Silicon Surface

Having chosen a low temperature solder and a desired thickness of thesolder joint, a technical problem remains as to how one solders totitanium and to silicon. As is known, neither of these elements will wetor adhere to known soldering materials. In embodiments, this may beaccomplished as follows. First, the silicon oxide coating on the MEMSchip (this coating is always on any silicon surface) may be removedusing a hydrofluoric acid. Preferably, using Buffered Hydrofluoric Acid,which typically contains 30-50% Ammonium Fluoride and 5-10% Hydrofluoricacid. Second, one takes and sputters the joining surface of the MEMSmicropump—quickly, before the SiO2 surface reforms—with titaniumtungsten, which is an adhesion promoter. Alternatively, treatment withhydrofluoric acid may be omitted if the joining surface of the MEMSmicropump is sputtered with titanium silicide. This is because theTitanium silicide breaks up the silicon oxide.

Finally, in embodiments, a layer of nickel may be deposited. However,because nickel will form an oxide layer upon storage in air, and thusnot wet to solder, gold is added to protect the nickel surface. Duringsoldering, the gold layer dissolves into the solder—leaving a fullywetted nickel-solder interface. Thus, one ends up with a clean bottomsurface on the MEMS chip of titanium tungsten (Ti—W), nickel and gold.It is here understood that it is actually the nickel that is beingsoldered to, the gold merely protecting the nickel from oxidation.

Still alternatively, in embodiments, the titanium tungsten may beomitted, and following the treatment of the silicon pump surface withhydrofluoric acid, a layer of nickel may be deposited, followed by alayer of gold.

B. Preparing the Titanium Manifold Surface for Soldering:

Having prepared the silicon pump surface, next described is preparationof the titanium manifold surface. Titanium metal forms a dense stableoxide which does not wet to solder. Therefore, in order to create asurface that will wet to solder, in embodiments, the surface of thetitanium may be ground flat with a 1000 grit finish, and electrolessnickel plated onto the titanium. Electroless nickel makes a weakadhesive bond to titanium oxide. Therefore, in order to achieve a strongmetallurgical attachment of the nickel to the underlying titanium, themanifold with the nickel plating may be heated, for example, to about400° C. for 30-60 minutes. At this temperature, the titanium oxidebreaks down and the nickel alloys with the titanium, resulting in atransition zone on the top of the manifold from titanium to nickeltitanium alloy to a pure nickel surface.

In embodiments, in order to protect the nickel surface from oxidation,as described above in the preparation of the silicon MEMS pump, themanifold may be further coated with gold. This process may be performed,for example, in a sputtering chamber. To do this, the nickel surface isfirst cleaned with an ammonia containing cleaning agent and thensputtered with another layer of nickel, and finally, a layer of gold.The additional layer of nickel is added because sputtered nickel adhereswell to nickel, even with a small amount of oxide. So, in embodiments, asecond layer of nickel may be sputtered onto the first layer in case thebaking operation described above (of the electroless nickel plated ontothe titanium) has created such a thick oxide that it is not easilywetted. Following the sputtering of the second layer of nickel, themanifold may be immediately gold plated.

Soldering the Treated Silicon Surface of the Pump to the TreatedTitanium Surface of the Manifold

Once both surfaces have been prepared, as noted above, a preform ofindium silver, comprising three percent silver and ninety-seven percentindium, which has a very low melting point, may be used in a solderingoperation in forming gas. Forming gas is a reducing agent and removesoxidation from any of the metallic surfaces. Generally, forming gascomprises 10% H₂ and 90% N₂, and this may be used for the solderingprocess. In embodiments, this temperature may be controlled to be in therange of 140° C. to 160° C. in order to:

-   -   Minimize the strain due to the CTE by limiting the temperature        excursion;    -   Prevent depolarization of the piezo ceramic actuator (615 in        FIG. 6) which occurs at approximately 200° C.; and    -   Prevent relieving the epoxy pre-stress that is part of the        operational design of the actuator that occurs at temperatures        above 160° C.

It is also noted that a filter may be loaded into the back of thetitanium manifold, shown, for example at 655 in FIG. 6. In embodiments,the filter may be a 5u filter to prevent particle entry into the pump,and may, for example, be made from a large variety of polymers, metalsor silicon.

FIG. 17A is a vertical cross-section of a Silicon Pump 1702 joined to aTitanium Manifold 1730 according to an embodiment. It illustrates threealternate joints that may be used in embodiments to join Silicon Pump1702 to Titanium Manifold 1730. These may be, with reference to FIG.17A, a fillet joint 1705 or a planar joint 1735. Alternatively, as shownat the bottom of the figure, a trough joint 1745 may be used to joinSilicon 1737 to the titanium manifold. It is noted that the advantage ofthe fillet and the trough designs is that the titanium, which has agreater CTE than silicon, as noted above, (CTE for Ti of 9.5 ppm/° C.versus 2.6 ppm/° C. for Si) will shrink around the indium solder and thesilicon MEMS pump, thus putting the silicon and titanium interfaces (asprepared) in compression, and as a result, there will be no forcetending to separate the pump from the manifold. However, the filletjoint places shear stress on the titanium solder joint. The trough hasno surfaces with shear or tension. As a result, the springs and pump capmay be eliminated in these designs. However, the sputtering process,which is line of sight, may be more difficult for trough joints. As maybe seen in FIG. 17A, between the pump and manifold are provided twoO-rings 1715, one surrounding the inlet (right side, vertical), theother surrounding the outlet (left side, with 90 degree elbow).

FIG. 17B depicts an exploded detail view of a pump assembly, O-rings,manifold and circuit connection board according to an exemplaryembodiment of the present invention.

FIGS. 17C through 17E illustrate further details of the three alternatejoint types shown in FIG. 17A, shown in a vertical cross section throughan exemplary pump assembly and manifold joined together. FIG. 17Cillustrates the fillet type joint, FIG. 17D the planar or flat joint,and FIG. 17E the trough type joint.

Referring now to FIG. 17F, this illustrates exemplary inlet and outletfilters for a MEMS pump according to embodiments. In embodiments, thesestay sealed from the moment the pump is built in a clean room.

FIGS. 17G and 17H illustrate an alternate concept for a configurationusing an adhesive (dispensed or pressure sensitive layer) to attach afilter and replace the O-rings in the embodiment shown in FIGS. 1-17E,In embodiments, the filter may be polycarbonate, polyether sulphone, oralternatively, a polyamide etched track filter with 5 micron holes orsmaller. In embodiments, the adhesive may be silicone or acrylic based.As may be seen in FIG. 17G, the preform (Indium silver) may be thickerthan the adhesive layer.

FIG. 17H depicts the example of FIG. 17G in a top perspective view. Inembodiments, there may be two separate inlet and outlet adhesives (withfilters). This allows each flow path to be tested separately.

FIG. 17I is a photograph of an actual MEMS pump attached to a titaniummanifold, in an embodiment similar to that of FIGS. 1-17, without thesprings or pump cover. The depicted device is similar to the view shownin FIG. 5, but without the springs, and easily seen is the gold platingon the manifold's upper surface, as well as the solder joint around theperiphery of the pump assembly. This example used a trough joint.

FIGS. 18-26 depict alternate examples of attaching a MEMS pump to atitanium manifold, according to an exemplary embodiment of the presentinvention. With reference to FIG. 18, an exemplary MEMS pump assembly isshown on top and an exemplary titanium manifold is shown on the bottomof the figure, each with a layer to be attached to the top and bottomsurfaces to be joined. FIG. 18 thus illustrates essentially the sameprocess as described above, but without the gasket. In this embodiment,it is noted, the fluid seal between inlet and outlet is not accessiblefor testing. In such embodiments, a reliable enough seal between inletand outlet may be obtained without the use of a double O-ring, whichmakes for a more cost-effective design. Here the indium layer is platedon the underside of the silicon pump, and brazed to the manifold, whichhas been prepared as described above, ultimately with a gold plating ontop. FIGS. 19 and 20 depict the same process as is shown in FIG. 18,from different views.

FIGS. 21-22 present another gasketless configuration using anindium-silver soldering joint, a gold thermo-compression bond, or aglass seal. In FIG. 21 a gold “monorail” on the pump bottom, surroundingthe pump inlet and outlet, is brazed to a gold plated layer on thetitanium manifold. In FIG. 22 an indium layer plated on the manifold isbrazed to the bottom surface of the pump assembly.

FIGS. 23 and 24 depict a similar process as the one shown in FIGS. 1-17,and described above with reference to those figures, except in place oftwo O-rings a silicone rubber gasket is used to doubly seal the inletfrom the outlet. An indium frame plated onto the top of the manifold isbrazed to a gold plate layer on the underside of a pump assembly. Thus,the silicone gasket seals around the pump inlet and outlet, and a brazeholds the pump to the manifold, as shown.

FIGS. 25 and 26 illustrate yet an alternate process wherein all of thesolder joints are replaced with a glass seal or a goldthermo-compression bond. It is noted, however, that the CTE and greatertemperature excursions needed for a glass joint, as well as the limitedability of these materials to accommodate strain, makethermo-compression bonding and glass seals somewhat less desirable.Further, because the temperatures for these processes also exceed theCurie point of the piezo actuator as well as the epoxy that holds it inplace, in these embodiments the processing steps may be reordered tocreate the manifold-MEMS pump joint first. Thus, in such embodiments,the glass frit, or thermo-compression bonding, would be done before thepiezoelectric actuator is epoxied to the silicon MEMS pump; otherwisethe frit and thermo-compression bonding temperatures would damage boththe piezo and the epoxy. This can add complexity and cost in suchembodiments.

As shown in FIGS. 25 and 26, in embodiments, a glass seal could be used1:1 in place of the braze described above with a different surfacepreparation. In embodiments, to prepare a surface for glass sealing, thejoint would need to be a trough design to avoid CTE cracking.

Finally, it is noted that thermos-compression bonding is possible with athickness similar to the indium thickness gold layer and a goldprojection from one of the surfaces.

However Au—Au bonding requires a temperature of 300° C. This is wellabove the Curie Point for the peizo actuator and the softening point forthe epoxy.

Example Silicon and Metal Surface Preparatory Processes

The following presents two example processes for preparing pumps andmanifolds for soldering, according to embodiments of the presentinvention. In embodiments, the techniques may be used for any siliconand metallic surfaces that are desired to be soldered together. Thefirst example describes a Ni/TiW/Au process for micro-pump chips, andthe second a TiW/Ni/Au process for micro-pump chips. Each of the twomicro-pump chip processes is followed by a protocol for preparing atitanium manifold (the same in each example). These exemplary processesmay, in embodiments, be used in the assembly of a microfluidic device,such as is illustrated in FIGS. 1 and 2, described above.

A. Pump and Manifold Solder Metalization Process for Ni/TiW/Au onMicro-Pump Chips:

-   -   1. Have blue-tape pieces pre-cut and ready    -   2. Take pump off of gel-pak and place under stereoscope on soft        towel or gelpak    -   3. Under scope, use tweezers to place tape as close as possible        to desired position    -   4. Make sure tape is pressed uniformly on surface (this will        prevent liquid surface treatment chemical from getting under the        tape and into the pump orifices)    -   5. Go to HF acid bench and prepare large dish with DI water for        rinse.    -   6. Using a polyethylene pipette, place enough BHF (Buffered HF,        8% HF) to coat masked surface with a bead of acid.    -   7. Wait until acid recedes from silicon surface and forms a bead        on the tape.    -   8. Place in the DI water to rinse. Rinse for 15 seconds. Dry        with N2 gun, both sides.    -   9. Place samples with piezo-side down onto blue tape and cut        around edges (this blue tape will make it easy to remove from        the carrier when sputtering is done)    -   10. Use a small piece of 2-sided Kapton tape on a carrier wafer        for each pump.    -   11. Place each pump unit on the 2-sided tape and make sure parts        are stably attached.    -   12. Load into AJA sputtering system.    -   13. Prior to sputtering on sample, condition Ni, TiW, Au targets        for 3 minutes under normal operation with shutter closed.    -   14. Conditions and rates for materials        -   a. AJA sputter 3, 44 on height, 4 on gun tilt.        -   b. Ni: 25 sccm Ar, 3 mT, 200 W, 9.4 nm/min        -   c. TiW: 25 sccm Ar, 4.5 mT, 300 W, 10 nm/min (make sure            voltage in compliance and stable)        -   d. Au: 25 sccm Ar, 10 mT, 300 W, 45 nm/min    -   15. Sputter using time to following thicknesses        -   a. TiW: 50 nm        -   b. Ni: 250 nm        -   c. Au: 1000 nm    -   16. Remove samples from sputter system    -   17. Using proper tweezers (small tip with jagged grip ends),        under stereoscope, carefully remove protective tape from pump        part. Metal may flake a little at the corner while first        grabbing tape.    -   18. Lift pump off of carrier and remove blue tape from        piezo-side of pump.    -   19. Place face down in a new, clean gelpak to keep pump orifices        clean of particulates.

Process for Ti-Manifolds:

-   -   1. Have manifold-tape pieces pre-cut and ready    -   2. Take manifold out of package    -   3. Go to acid bench and prepare large dish with DI water for        rinse.    -   4. Mix NH₄OH (30% concentration):DI Water 1:2 in a small beaker.    -   5. Hold sample upside down with tweezers so that surface is in        base.    -   6. Let sit for 30 s.    -   7. Place in the DI water to rinse. Rinse for 30 seconds. Dry        with N2 gun, both sides. Make sure to dry holes thoroughly.    -   8. Under scope, use tweezers to place tape as close as possible        to desired position    -   9. Make sure tape is pressed uniformly on surface    -   10. Use small piece of blue tape to protect side hole (larger        one with smaller hole in center)    -   11. Place samples with non-protected-side down onto blue tape        and cut around edges (leave 2 sides of tape exposed for mounting        to carrier wafer)    -   12. Use Kapton tape to hold manifolds on carrier by taping over        the exposed blue tape.    -   13. Load into AJA sputtering system.    -   14. Prior to sputtering on sample, condition Ni, Au targets for        3 minutes under normal operation with shutter closed.    -   15. Conditions and rates for materials        -   a. AJA sputter 3, 44 on height, 4 on gun tilt.        -   b. Ni: 25 sccm Ar, 3 mT, 200 W, 9.4 nm/min        -   c. Au: 25 sccm Ar, 10 mT, 300 W, 45 nm/min    -   16. Sputter using time to following thicknesses        -   a. Ni: 2 minutes for about 20 nm        -   b. Au: 22 minutes for about 1000 nm    -   17. Remove samples from sputter system    -   18. Using proper tweezers (small tip with jagged grip ends),        under stereoscope, carefully remove protective tape from pump        part. Metal may flake a little at the corner while first        grabbing tape.    -   19. Cut manifold off of carrier. Leave blue tape on bottom to        protect from particles.    -   20. Place face down in a new, clean gelpak to keep orifices        clean of particulates.

B. Process for TiW/Ni/Au on Micro-Pump Chips:

-   -   1. Have blue-tape pieces pre-cut and ready    -   2. Take pump off of gel-pak and place under stereoscope on soft        towel or gelpak    -   3. Under scope, use tweezers to place tape as close as possible        to desired position    -   4. Make sure tape is pressed uniformly on surface (this will        prevent liquid surface treatment chemical from getting under the        tape and into the pump orifices)    -   5. Go to HF acid bench and prepare large dish with DI water for        rinse.    -   6. Using a polyethylene pipette, place enough BHF (Buffered HF,        8% HF) to coat masked surface with a bead of acid.    -   7. Wait until acid recedes from silicon surface and forms a bead        on the tape.    -   8. Place in the DI water to rinse. Rinse for 15 seconds. Dry        with N2 gun, both sides.    -   9. Place samples with piezo-side down onto blue tape and cut        around edges (this blue tape will make it easy to remove from        the carrier when sputtering is done)    -   10. Use a small piece of 2-sided Kapton tape on a carrier wafer        for each pump.    -   11. Place each pump unit on the 2-sided tape and make sure parts        are stably attached.    -   12. Load into AJA sputtering system.    -   13. Prior to sputtering on sample, condition Ni, TiW, Au targets        for 3 minutes under normal operation with shutter closed.    -   14. Conditions and rates for materials        -   a. AJA sputter 3, 44 on height, 4 on gun tilt.        -   b. TiW: 25 sccm Ar, 4.5 mT, 300 W, 10 nm/min (make sure            voltage in compliance and stable)        -   c. Ni: 25 sccm Ar, 3 mT, 200 W, 9.4 nm/min        -   d. Au: 25 sccm Ar, 10 mT, 300 W, 45 nm/min    -   15. Sputter using time to following thicknesses        -   a. TiW: 50 nm        -   b. Ni: 250 nm        -   c. Au: 1000 nm    -   16. Remove samples from sputter system    -   17. Using proper tweezers (small tip with jagged grip ends),        under stereoscope, carefully remove protective tape from pump        part. Metal may flake a little at the corner while first        grabbing tape.    -   18. Lift pump off of carrier and remove blue tape from        piezo-side of pump.    -   19. Place face down in a new, clean gelpak to keep pump orifices        clean of particulates.

Process for Ti-Manifolds:

-   -   1. Have manifold-tape pieces pre-cut and ready    -   2. Take manifold out of package    -   3. Go to acid bench and prepare large dish with DI water for        rinse.    -   4. Mix NH₄OH (30% concentration):DI Water 1:2 in a small beaker.    -   5. Hold sample upside down with tweezers so that surface is in        base.    -   6. Let sit for 30 s.    -   7. Place in the DI water to rinse. Rinse for 30 seconds. Dry        with N2 gun, both sides. Make sure to dry holes thoroughly.    -   8. Under scope, use tweezers to place tape as close as possible        to desired position    -   9. Make sure tape is pressed uniformly on surface    -   10. Use small piece of blue tape to protect side hole (larger        one with smaller hole in center)    -   11. Place samples with non-protected-side down onto blue tape        and cut around edges (leave 2 sides of tape exposed for mounting        to carrier wafer)    -   12. Use Kapton tape to hold manifolds on carrier by taping over        the exposed blue tape.    -   13. Load into AJA sputtering system.    -   14. Prior to sputtering on sample, condition Ni, Au targets for        3 minutes under normal operation with shutter closed.    -   15. Conditions and rates for materials        -   a. AJA sputter 3, 44 on height, 4 on gun tilt.        -   b. Ni: 25 sccm Ar, 3 mT, 200 W, 9.4 nm/min        -   c. Au: 25 sccm Ar, 10 mT, 300 W, 45 nm/min    -   16. Sputter using time to following thicknesses        -   a. Ni: 2 minutes for about 20 nm        -   b. Au: 22 minutes for about 1000 nm    -   17. Remove samples from sputter system    -   18. Using proper tweezers (small tip with jagged grip ends),        under stereoscope, carefully remove protective tape from pump        part. Metal may flake a little at the corner while first        grabbing tape.    -   19. Cut manifold off of carrier. Leave blue tape on bottom to        protect from particles.    -   20. Place face down in a new, clean gelpak to keep orifices        clean of particulates.

Illustrative examples of the technologies disclosed herein are providedbelow. An embodiment of the technologies may include any one or more,and any combination of, the examples described below.

1-37. (canceled)
 38. A microfluidic device, comprising: a silicondevice; and a metallic component, wherein the silicon device and themetallic component are attached by: preparing a surface of a silicondevice to be solderable; preparing a corresponding surface of a metalliccomponent to be solderable; and soldering the prepared surface of thesilicon device to the corresponding prepared surface of the metalliccomponent with a solder of a pre-defined composition and thickness toaccommodate strain due to co-efficient of thermal expansion (CTE)mismatch between the silicon device and the metallic component.
 39. Themicrofluidic device of claim 38, wherein at least one of: the silicondevice is a MEMS pump; the metallic component is a titanium manifold;the solder is deposited between the surfaces in a defined thickness todistribute overall shear strain through the solder joint; or the solderis deposited between the surfaces in a defined thickness to distributeoverall shear strain through the solder joint and the pre-definedthickness is such that the strain of the solder joint does not exceedthe shear strength of the solder.
 40. The microfluidic device of claim38, wherein the silicon device is a MEMS pump, the metallic component isa titanium manifold, and wherein: a lower surface of the MEMS pump isprepared by: removing a silicon dioxide coating; sputtering the joiningsurface of the MEMS pump with an adhesion promoter; depositing a layerof nickel; and depositing a layer of gold onto the nickel.
 41. Themicrofluidic device of claim 38, wherein the silicon device is a MEMSpump, the metallic component is a titanium manifold, and wherein: anupper surface of the metallic component is prepared by: grinding thesurface flat; plating electroless nickel onto the surface; heating thenickel plated surface to a temperature where any metallic oxide breaksdown and the nickel alloys with the surface; coating the surface withgold.
 42. A method of permanently attaching a silicon device to ametallic component, comprising: preparing a surface of a silicon deviceto be solderable; preparing a corresponding surface of a metalliccomponent to be solderable; and soldering the prepared surface of thesilicon device to the corresponding prepared surface of the metalliccomponent with a solder of a defined composition, and of sufficientthickness, to accommodate strain due to co-efficient of thermalexpansion (CTE) mismatch between the silicon device and the metalliccomponent.
 43. The method of claim 42, wherein at least one of: thesilicon device is a MEMS pump, the metallic component is a titaniummanifold, and the MEMS pump and the titanium manifold are provided in amicrofluidic device; the solder is deposited between the surfaces in apre-defined thickness to distribute overall shear strain through thesolder joint; or the solder is deposited between the surfaces in apre-defined thickness to distribute overall shear strain through thesolder joint, and the pre-defined thickness is such that the strain ofthe solder joint does not exceed the shear strength of the solder. 44.The method of claim 42, wherein the silicon device is a MEMS pump havingan upper surface and a lower surface, the metallic component is atitanium manifold, and a lower surface of the MEMS pump is prepared by:removing a silicon dioxide coating; sputtering the joining surface ofthe MEMS pump with an adhesion promoter; depositing a layer of nickel;and depositing a layer of gold onto the nickel.
 45. The method of claim44, wherein at least one of: the silicon dioxide coating is removed bybuffered hydrofluoric acid; the adhesion promoter is titanium tungsten;or a lower surface of the silicon device is prepared by: sputtering thejoining surface of the silicon device with a metallic silicide;depositing a layer of nickel; and depositing a layer of gold onto thenickel.
 46. The method of claim 42, wherein the silicon device has alower surface, and wherein the lower surface is prepared by either:removing a silicon dioxide coating with an acid wash; depositing a layerof nickel; and depositing a layer of gold onto the nickel, or removing asilicon dioxide coating with buffered hydrofluoric acid; depositing alayer of nickel; and depositing a layer of gold onto the nickel.
 47. Themethod of claim 42, wherein at least one of: the metallic component hasan upper surface, and the upper surface is prepared by: grinding thesurface flat; plating electroless nickel onto the surface; heating thenickel plated surface to a temperature where any metallic oxide breaksdown and the nickel alloys with the surface; and coating the surfacewith gold, or the metallic component is a titanium manifold having anupper surface, and the upper surface is prepared by: grinding thesurface flat with a 1000 grit finish; plating electroless nickel ontothe surface; heating the nickel plated surface to a temperature whereany metallic oxide breaks down and the nickel alloys with the surface;and coating the surface with gold.
 48. The method of claim 47, whereinat least one of: the nickel plated surface is heated to between 375 and425° C. for between 30 and 60 minutes; the nickel plated surface isheated to a temperature and for a time such that any titanium oxidebreaks down and the nickel alloys with the titanium, resulting in atransition zone on the top of the manifold from titanium to nickeltitanium alloy to a pure nickel surface; or said coating the surfacewith gold includes cleaning the nickel surface with an ammoniacontaining cleaning agent followed by sputtering the nickel surface withanother layer of nickel, followed by a layer of gold.
 49. The method ofclaim 42, wherein at least one of: the solder is an indium silversolder; the solder is an indium silver solder, wherein the soldercomprises 97% Indium and 3% silver by weight; the solder melts at atemperature no greater than 160° C.; or the soldering is controlled tooccur at a temperature between 140° C. and 160° C.
 50. The method ofclaim 42, wherein the metallic component has an upper surface, and theupper surface is prepared by: grinding the surface flat; platingelectroless nickel onto the surface; heating the nickel plated surfaceto a temperature where any metallic oxide breaks down and the nickelalloys with the surface; coating the surface with gold.
 51. The methodof claim 50, wherein metallic component is a titanium manifold, andwherein at least one of: the surface of the titanium is ground flat witha 1000 grit finish; the nickel plated surface is heated to between 375and 425° C. for between 30 and 60 minutes; or the nickel plated surfaceis heated to a temperature and for a time such that any titanium oxidebreaks down and the nickel alloys with the titanium, resulting in atransition zone on the top of the manifold from titanium to nickeltitanium alloy to a pure nickel surface.
 52. The method of claim 50,wherein at least one of: coating the surface with gold further comprisescleaning the nickel surface with an ammonia containing cleaning agentfollowed by sputtering the nickel surface with another layer of nickel,followed by a layer of gold; the solder is an indium silver solder,comprising 97% Indium and 3% silver by weight; the solder melts at atemperature no greater than 160° C.; or the soldering is controlled tooccur at a temperature between 140° C. and 160° C.